Tuesday, 11 January 2005: 8:45 AM
Climate change commitment in the 21st and 22nd centuries in the CCSM3 global coupled climate model
The concept of climate change commitment is explored with the latest version of the Community Climate System Model (CCSM3). We address the following question that has been posed for the IPCC Fourth Assessment Report: In a transient climate simulation with a global coupled climate model, if concentrations of all atmospheric constituents were suddenly held fixed or “frozen”, how much more additional warming would we be committed to? Thermal inertia in the coupled climate system dictates that warming will continue even if we could stabilize concentrations of greenhouse gases, and we quantify this warming commitment for three different commitment scenarios. This concept has policy implications in that the longer we wait to stabilize concentrations of greenhouse gases, the more warming we are committed to. Five member ensembles of 20th, 21st and 22nd century climate simulations are analyzed, where 1) concentrations of all radiatively active constituents are frozen at year 2000 values for the next 100 years, and 2) the SRES A1B 21st century climate change scenario and 3) SRES B1 experiments to the year 2100 have their concentrations held fixed at year 2100 values for another 100 years. Results show that the trajectory of concentrations prior to freezing concentrations affects the climate change commitment. The end of 20th century has steepest increase of concentrations of greenhouse gases (and most subsesquent warming commitment in the model), followed by A1B and then B1, each with progressively more stabilized concentrations before the year 2100, and consequently less warming commitment.